This invention relates to sheet coating machines, that is to say to machines for coating sheets with a variety of substances most of which include high quantities of volatile organic solvents which are evaporated off and incinerated during a following curing process in a thermal drying oven. However, very significant amounts of solvent vapourise at the machine, and health and safety regulations require that these are not dissipated into the atmosphere but are incinerated.
It is well known to enclose the coating machine entirely within a front extension of the oven, thus containing the solvent emissions from the machine within the oven. However, this arrangement has the disadvantages that the atmosphere within the extension must be acceptable to an operator working therein for the purposes of setting and checking the machine, but the size of the extension requires that a high rate of air flow into it is needed to keep the atmosphere acceptable, which in turn lowers the thermal efficiency of the oven; and that machine elements and coating substances have to be transported into and handled within the confines of the extension.
It is also known to enclose the coating machine entirely within a sizeable chamber separate from the oven, to provide a tunnel connecting the chamber and the oven through which the sheets are transported, and to provide an extraction system for the chamber. This arrangement suffers from the same disadvantages as the arrangement referred to in the preceding paragraph.
There has also been produced hitherto a coating machine with a hood above it enabling vapours to be contained within the working area and having two covers which could be raised to provide access to said area. An extraction system was mounted above the machine on or adjacent to the hood between the covers, drawing the vapours upwardly. This arrangement has the disadvantages that the hood and the extraction system hinder the installation and use of a hoist for enabling machine elements to be changed; that extraction is less effective because the vapours are heavier than air; and that during setting and checking of the machine when one or both of the covers is or are raised and the extraction system is still in operation, vapours are drawn upwardly past the head of the operator.
The object of the present invention is to avoid all of the disadvantages hereinbefore referred to.
The invention comprises a sheet coating machine in which sheets are fed along a bed through a working area where they are given a coating of a volatile substance to an adjoining oven where the coating is cured, at least one cover which is moveable to provide access when necessary to the working area and which enables vapours produced by evaporation from the substance to be contained within the working area, air inlet means which enable the vapours to be extracted for incineration, and suction means which are arranged to extract the vapours downwardly from within the working area.
The working area preferably comprises a coating station having a moveable cover which provides access when necessary to the coating station.
Preferably, the air inlet means of the coating station comprise vents in the moveable cover.
Preferably, also, the coating station is provided with a base, walls along its sides, and upstream and downstream baffle plates across its ends in order to contain the vapours within the coating station, the baffle plates being adapted to permit feeding of the sheets along the bed.
Preferably, the working area comprises also a sheet reject station disposed between the coating station and the oven and having another moveable cover which provides access when necessary to the sheet reject station.
Preferably, also, the sheet reject station is provided with a floor, walls along its sides, and upstream and downstream baffle plates across its ends in order to contain the vapours within the sheet reject station, the baffle plates being adapted to permit feeding of the sheets along the bed.
Preferably, the walls of the sheet resect station are continuations of the walls of the coating station, and the upstream baffle plate of the sheet reject station and the downstream baffle plate of the coating station are one and the same element.
Preferably, also, the air inlet means of the sheet reject station comprise vents in a reject sheet withdrawal door in one of the walls.
Preferably, the suction means which are arranged to extract the vapours downwardly comprise ducts connected to the base of the coating station, to the sheet reject station, to a gearbox for driving the machine, and to a housing for a replaceable tank from which the substance is supplied to the coating station.
Preferably, also, the ducts communicate with a common duct in the base of the machine leading to an upper zone of the oven.
The sheet coating machine is preferably provided with a hoist for enabling machine elements to be changed which is disposed above the working area and is completely unimpeded by the suction means which are arranged to extract the vapours downwardly.